Bungee shock cords are commonly used tools found in many different applications. These tools are composed of many elastic strands that are encased in a woven sheath. A bungee shock cord is also referred to as an elastic cord, shock cord, and just bungie. The strands inside a shock cord are constructed from natural rubbers or manufactured rubber. In some instances, the internals are composed of both. You should choose an inner cord material based on the intended use of the cord.
The outer sheath is also composed of different materials based on the needs of the user. The most common materials include nylon, cotton, and polypropylene. The outer sheath protects the inner strands, but the outer sheath also facilitates uniform stretching.
The decision made about inner and outer materials directly results in the bungee shock cord's stretching capabilities. When shopping, the elongation capacity is seen as the percentage compared to the unstretched length. Under these circumstances, a cord with 100% elongation can stretch to double its original length.
When shopping for bungee shock cords, you should not just think about the elasticity. Of course, how the cord stretches is important, but you also need to consider the outer materials to protect the inner strands. Can your bungie operate in the environments you need? If using the cord predominantly outdoors, polypropylene offers strong UV protection. If used in marine environments, consider using nylon.